The electrical conduction properties of normal and damaged cat peripheral nerves were studied longitudinally using chronically implanted, multi-contact nerve cuff electrodes. The effects of chronic nerve constrictions were similar to clinical dying-back neuropathy, including distal shrinkage and slowing in less severe cases and complete degeneration with proximal dilatation in more severe cases. Regeneration following complete crush lesions could be accurately followed at the single unit level by using stimulus-triggered averaging, with the surprising result that the earliest and fastest regenerating fibers appeared to rise from Group II stem axons rather than the larger Group I fibers. Recovery from a crush combined with a constriction showed significant slowing of both the growth and maturation of regenerating fibers, but eventually recovery was complete.